Disk drive memory systems ("disk drives") have been used to store information for computers, word processors, computer controlled information retrieval systems and the like, for many years. In disk drives, information, usually in forms of digital electronic signals, is recorded on concentric memory tracks on magnetic disks. As is well known in the art, there are two basic kinds of disk drives: "floppy" disk drives and "hard" disk drives. In both kinds of disk drives, disks are rotatably mounted on a spindle. Read/write heads, generally located on pivoting arms, move radially over the surface of the disks to access different memory locations. There may be as many as 800 or more memory tracks per radial inch of a disk. Each track is also divided into a plurality of sectors, 36-72 sectors for example, and each sector can store a plurality of bytes of digital data, typically 512 bytes or 1,024 bytes.
To ensure proper writing and reading of the information, a read/write head must be accurately aligned with an appropriate track on a disk. Floppy disk drives store information on interchangeable, flexible and magnetic disks. Hard disks store information on rigid non-interchangeable disks (but, can be interchangeable), commonly made of aluminum coated with magnetic material. Hard disks have a much higher storage density than floppy disks, and as a consequence, hard disk drives require more accurate positioning capabilities of magnetic heads on the surface of the hard disk than that of the floppy disk drive.
Disk drives, especially small form factor disk drives are often located within the housing of a computer and receive instructions from the host computer to read/write information on the disk. The small form factor disk drives may comprise multiple hard disks stacked on top of each other within the drive for increasing memory capacity. The disks are spun at high speeds, for example 3,600 rpm (revolutions per minute), by a spindle motor to allow rapid writing and reading of information on the disk.
The advent of personal and portable computer systems which are sometimes called "laptop computers" or "notebook computers", has placed a premium on providing disk drives of reduced size and weight. The relative size of disk drives is commonly referred to as its form factor. Form factors of 2.5 inches (6.25 cm) and even smaller have become relatively commonplace.
In addition to reducing size and weight of the disk drives in connection with the laptop computers, it is also important to make available electric power saving features since laptop and notebook computers are typically battery-powered, and it is desirable to reduce battery drain. Namely, because of the reduction of the power consumption in the computers by the development of semiconductor technology, it has become possible to power the computers by batteries. Further, the recent computers are so compact that the requirements arise in carrying the computers anywhere without a commercial power source or power outlets. Thus, it is extremely important that power dissipation in the disk drives be minimized so that the computers can be operable for a longer period time by relatively small batteries.
Furthermore, in the computer systems, there are always requests by users for increasing a speed of a disk drive. One factor for increasing the speed of the disk drive is to reduce an access time of the disk drive. The access time is a time required for the disk drive to start performing the read/write operation after receiving the instructions from the host computer. The access time includes a seek time which is a time required for the magnetic head changes its position from one place to another on the magnetic disk. In reality, the seek time accounts for the most of the access time since it involves a mechanical movement which is clearly slower than the electrical operation. In a typical small factor disk drive, an access time ranges from 15 millisecond to 30 millisecond.
Other requirements in disk drives associated with speed of the operation is a spindle motor starting time which is a time required for the spindle motor to start rotation and reach to the rated rotation speed. This type of operation arises when the disk drive is initiated from a "sleep" state or a "standby" state, wherein the spindle motor is not provided with electric power and thus it is at rest (non-rotation state). Thus, it is important in such disk drives to reduce a transient time (or settling time) required for the spindle motor starting from the non-rotation state to reach a predetermined rotation speed. However, the time required for the spindle motor to reach the predetermined rotation rate is relatively large, such as 15-30 seconds, which is thousand times larger than the access time. There is a further interest directed to reducing the peak starting current of the spindle motor for eliminating the adverse effect to the battery and thus increasing the battery life.
In such a disk drive, major parts of the drive that dissipate most of the electric power are, a spindle motor for rotating the disk in high speed, an actuator assembly for driving the magnetic heads to the designated position on the disk for reading and writing data, and disk drive electronics (i.e., an electronic circuit) for controlling the operation of the disk drive. In one portable computer system, it is known to reduce power usage by powering down certain of the disk drive electronics upon the occurrence of a single, predetermined event or condition. U.S. Pat. No. 4,568,988 to McGinlay et al. shows an example of reduction of power dissipation by such powering down. Namely, McGinlay et al. discloses means for reducing current drawn by a stepper motor when the disk drive has been deselected for more than a predetermined time length such as two seconds.
Further improved means for reduction of the electric power dissipation is disclosed in U.S. Pat. No. 4,933,785 to Morehouse et al. issued Jun. 12, 1990. In Morehouse et al., two power saving modes are provided. One mode involves maintaining power to a disk drive intelligent interface electronics, disk controller and a spin motor assembly while powering down virtually all other electronics. In this mode, the disk drive microprocessor is maintained in a low power mode, i.e., it is not consuming power due to changing binary states. Under software control, this mode of operation is invoked using a default time, for example, five seconds after the last disk access by the read/write head.
The second mode for lowering the power consumption in this prior art is a spun down deselected mode in which only the disk drive intelligent interface and disk controller are fully powered. In this mode, not only is the disk drive microprocessor in its lower power state but the spin motor assembly is powered down. This mode of operation is invoked using a longer default time, for example, 20 seconds after the last disk access.
However, these prior disk drives do not give consideration to large power consumptions by transient currents. The transient currents include dynamic currents flowing especially at the start of mechanical movement of a spindle motor and the magnetic head when the spindle motor starts rotation and the magnetic head changes position from one position to other. Any disk drive in the market includes a spindle motor for rotation of the magnetic disk and an actuator for accessing the magnetic head from one place to another on the disk. These spindle motor and actuator require driving coils for generating forces to drive magnets or magnetic circuits therein. Therefore, a relatively large amount of current flows when the motor is driven from its static state to start rotation and attain its constant velocity state. Also, relatively large current flows when the actuator is driven from its read/write state at one position to another position.
Because the electrical power consumption in the electronic circuits has been remarkably decreased because of the development in the semiconductor technology, the power consumption in the spindle motor drive and the actuator drive are major components that account for most of the power consumption in the disk drives. Furthermore, because the actuator drive and the spindle motor utilize coils for generating magnetic fields, large transient currents (peak currents) flow through the coils at the initiation of such movement. It is well known in the art that this type of large peak current or surge current will deteriorate battery life. Thus, it is important to reduce the transient current to elongate battery life.
In such disk drives, however, the relationship between the amount of transient current and time required to reach to the target conditions, i.e., the rated rotational speed of the motor and/or the destined position of the magnetic head is incompatible. Namely, if the transient current is reduced, a longer time is usually required for the motor to reach the predetermined steady state rotation rate. Similarly, if the transient current is reduced, longer access time or seek time (i.e., time required for the read/write head to reach from one location to another on the disk surface) is required for the actuator.
Therefore, in the prior art disk drives, reduced power requirements of the small form factor disk drives used in portable computers environments, such as laptop computers, creates a situation where the access time is increased to reduce power consumption in the disk or the power consumption is increased in order to decease the access time. Similarly, in the disk drives, the starting time of the spindle motor is increased to reduce the peak starting current or the peak starting current is increased in order to decrease the spindle motor starting time. In the spindle motor, however, if the spindle motor is initiated from a non-rotation state ("sleep mode" or "standby mode"), the reduction of the starting time is not very important since it takes several tens of seconds. Thus, in driving the spindle motor, it is more important to reduce the amount of peak drive current which can successfully overcome friction in the disk drive and bring the spindle motor into rotation.
Therefore, there is a need for a small form factor disk drive which is capable of further decreasing electric power consumption in the disk drive with an optimum access time of a read/write head which can be selective either by manufacturers or by the user of the disk drive. Also, there is a need for a small form factor disk drive which is capable of automatically selecting an optimum start up current for the spindle motor to minimize the start up current while overcoming resistance of sticktion in the disk drive.